Release sheets are widely used industrially. Examples of known release sheets include: materials for protecting or processing the pressure-sensitive adhesive/adhesive surfaces of pressure-sensitive adhesive materials such as pressure-sensitive adhesive sheets and pressure-sensitive adhesive tapes; processing materials for producing wiring boards such as printed wiring boards, flexible printed wiring boards and multilayer printed wiring boards; materials for protecting liquid crystal display components such as polarizing plates and retardation plates; and materials used for the purpose of forming sheet-shaped structures. Hereinafter, the objects to which release sheets are applied are referred to as “adherends.”
In general, examples of the structure of a release sheet include a structure as a film formed of a resin having a releasability, or a structure in which a release layer is laminated on a substrate such as a film or a paper.
Resins having releasability are generally expensive, and hence a release sheet such as the above-described film-shaped release sheet formed of such a resin as a single substance is disadvantageously expensive.
Accordingly, there have been proposed a large number of products in each of which a release layer is laminated on an inexpensive substrate by extrusion laminating or by coating.
However, such an extrusion laminating suffers from difficulty in forming a thin layer on a substrate to result in low cost-reduction effect, and also offers a problem with respect to the adhesion to the substrate.
The lamination by coating is an effective processing method for forming a thin release layer and various methods for such lamination are proposed.
For example, as the methods using a solvent-based coating agent, there have been proposed a method in which a vinyl group-containing polydimethylsiloxane is laminated (JP 2002-182037 A) and a method in which a fluorine compound is laminated (JP 2007-002066 A).
On the other hand, examples of a method using an aqueous release coating agent include methods in which a material such as a wax, a low molecular weight silicone compound or a fluorinated surfactant is laminated as a release layer. However, there occurs a disadvantage that when an adherend is peeled off from the release sheet, these release agents are transferred to the adherend to degrade the functions of the adherend such as the pressure-sensitive adhesiveness of the adherend.
As a countermeasure against the disadvantage, there have been proposed methods in which a silicone resin is laminated by coating (JP 07-196984 A, JP 2005-125656 A), a method in which a fluorine-containing resin is laminated (JP 2004-114620 A), methods in which a polyolefin resin having a specific composition is laminated (JP 2007-031639 A, JP 2002-265719 A), and a method in which laminated is a resin layer composed of a release agent obtained by reacting polyvinyl alcohol with a long chain alkyl compound and an acid-modified polyolefin copolymer (JP 09-104851 A).